Electrical contact.



C. PFESFFER.

ELECTRICAL CONTACT.

APPLICATION FILED NOV. 19. 1913:

m m w Patented Mar. 27,1917

ELECTRICAL CONTACT.

Application filed November 19, 1913.

To all whom it may commas.

Be it known that I, CHARLES PFEIFFER, a resident of Milwaukee, in thecounty of Milwaukee and State of Wisconsin, have invented certain newand useful Improvements in Electrical Contacts, of which the followingis a full, clear, and exact description.

The invention relates to electrical contacts and their method ofmanufacture, and more particularly to that type of contact whichincludes a body or element of carbonaceous material, such as graphite.

Heretofore, it hasbeen the practice to electroplate the sides and oneend of the carbonaceous element with an electrical conducting mediumsuch as copper, to provide a suitable contact surface which is adaptedto engage another contact or terminal. In practice the CilllJOlltHKXNlSconductors are raised to a high temperature and this causes the copperplate to become loosened, particularly when the thickness of the plateexceeds that used in the ordinary commercial plating, andv thisincreased thickness is desirable to withstand the mechanical stresses towhich it is subjected in carrying the current desired. An example ofthis type of contact and the manner of its use is set forth in LettersPatent No. 1,054,902, dated March 4, 1913.

in the use of graphite as an electrical conductor, some means isnecessary to make a satisfactory and durable contact with the metallicconductor or contact leading to or from the graphite conductor and thedoc tro-plating of conducting medium onto the graphite was designed forthis purpose.

I have found that carbonaceous material, such as graphite, which 'isused in this type of contact, may be compressed and that by pressing thegraphite element and the me tallic container together, a more ei'licicntcontact results than that produced by electro-plating. By thiscompression operation, an intimate contact between the graphite and themetallic conductor is obtained. at considerable pressure over arelatively large area and furthermore, this intimate contact ismaintained despite the expansion and contraction of the two elementswhen they are subjected to varying and high temperature when in use.

A further objection to the electroplating was that the processwasexpensive and re- Specification of Letters Patent.

Patented Mar. 2?, 19ft.

Serial No. 801,796.

quired av long time. By employing a sepa rate container and placing thegraphite body therein and compressing the two, a composite electrical.contact of high efficiency is produced and the contact may be quicklyand cheaply manufactured.

ther advantages and objects of the invention will be manifest from thecontact and. method of making the same, hereinafter set forth.

The invention consists in the several novel features hereinafter setforth and more particularly defined by the claims at the con clusionhereof.

In the drawings: Figure l is a View, showing the contactmember appliedto a resistance device. Fig. 2 is a sectional. View showing thecontact-member in position in a die before compressing it.. Fig. 3 is asectional view showing the contact member in position in a die after ithas been compressed.

The electrical contact 10 is illustrated in Fig. 1 as applied to the endof a resistance device, which comprises a resistor 1 within acontainil'ig chamber 2. The. resistor 1 is made up of a series ofresistance disks, which as a whole, make up the resistance element ofthe resistance unit. At the top of the series of resistance disks, aterminal is provided and a graphite disk 14 is placed in contact withthe top resistance disk. Upon the top of this disk 14, ismounted thecontact 10, which is secured to a terminal plug 16 by a screw 17 andserves as an electrical conductor between the terminal 16 and the disk14., the contact being placed so that the bottom face of the metalliccontainer abuts against the terminal 16.

The contact 10 comprises a body 11 of carbonaceous material, such asgraphite, held within an intimatily connected container 12 made ofconducting material, such copper. (The graphite body or element isprovided with an aperture 13 through which the screw 1? is inserted tosecure the contact 10 to the terminal 16. The aperture 13 is providedwith a shoulder 15 against which the head of the screw 17 abuts.

in manufacturing the contact 10, a cylindrical cup or container 12 isformed of drawn copper or other suitable conducting metal, the walls ofwhich are of the desired thickness, by pressing a ptece of plate ofgraphite conductor 11 and the depth of the cup 12 is such as to allowthe graphite conductor-element to project out far enough from the upperedge of the cup, as shown at 20 to prevent any contact between the cupand the adjacent plate or conductor 14,

upon which the graphite disk is to hear.

The cup 12 and the cylindrical graphite conductor-element containedtherein are then pressed into a cylindrical die 21 oi such dimensionsthat the metallic cup is pressed firml y around the graphite withsufficient force to reduce the diameter of both the metallic cup and thegraphite conductor contained therein.

' The result of this construction and mannor of making it, is a metallicconductor surface which intimately contacts with the graphite conductorelement; the metal aird the graphite being constantly under a yieldingpressure regardless of the relative changes of dimensions of themetallic cup and the graphite conductor due to the differentco-ellicientsof expansion of the materials when heated, or changes ofdimension from other causes. The metallic element of the contact can bemade of any. desired thickness, thereby afl'ording any amount ofmechanical strength and conductivity neccssary. r

The invention is not to be understood as restricted to the details setforth, since these may be modified within the scope of the appendedclaims without departing from the spirit and scope of the invention.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent, is:

1. The method of making composite electrical contact members,consisting. in connecting an elastic graphite element with a metallicconductor clement under suiiicicnt resilient pressure of one elementupon the other to compensate tor differences in expansion andcontraction due to the extreme cl'iang'es in temperature to which suchcon tact members are subjected and to maintain intimate pressure contactoia substantially cons'an'l. degree between the elements notwithstanding such temperature changes.

2. The method of making composite electrical contact members, whichconsists in subjecting a. body of elastic carbonaceous material toclamping pressure of a metallic container sutiicient to reduce thevolume of the portion of the carbonaceous material which the containerengages and develop suiiicient elastic reactionary pressure tomaintain'the carbonaceous element and the container in intimate pressurecontact under the varying temperature conditions to which such contactmembers are subjected.

3. That improvement in making a composite electrical contact memberwhich consists in uniting an elastic carbonaceous element with ametallic container by subjecting the container to sufiicient pressure todistort the container and density the carbonaceousmaterial thereinsuiiiciently to produce an elastic reaction against the container underall service conditions of temperature variations.

4-. An electrical contact composed of an elastic carbonaceous materialand a conducting device adapted 'to maintain said material in a state ofdistortion under all service conditions of varying temperature, andnotwith- I action.

6. An electrical contact composed of compressed carbonaceous material.and electrical conducting means adapted to maintain said material in astate of compression sufficient to reduce its volume under allconditions of working temperature notwithstanding differences in thenormal rate of thermal expansion and contraction of the carbonaceousmaterial and the conducting means.

7. An electrical contact composed of compressed elastic graphite andmeans for maintaining said graphite in a state of compres sion under allservice conditions of varying temperature. e

S. In an electrical contact, the combination of an elastic carbonaceousbody and a metallic container, having walls against which thecarbonaceous body resiliently cX- pands, said body being suiiicientlyelastic to maintain an eflective pressure upon the container undervarying temperature conditions.

S). That improvement in making an electrical contact-member, whichconsists in placing a body of an elastic carbonaceous material in ametallic container and subjecting the container and material to pressureso as to produce an intimate contact between the container and thecarbonaceous material, the pressure being suflicient to densify the bodyof carbonaceous material, and develop a. permanent reactionary pressureof said material upon the container.

10. That improvement in making an electrical contact member, avhichconsists in placing an elastic carbonaceous body or element in aseparately formed metallic eontainer of conducting material andsubjecting the container to pressure to contract it around thecarbonaceous element.

11. an electrical contact comprising an elastic carbonaceous body whichis com- ;ed and maintained in estate of coma surrounding member undertemperature conditions.

An electrical contact comprising an elastic carbonaceous body, which isc0md maintained in a state of com- )n by a surrounding metallic member,diameter of which is relatively increased diminished by changes '11temperature. 13. in an electrical contact, the combination of an elasticcylindrical carbonaceous be "y and a metallic cup, having a portionthereof compressed In saic l by the pressure of the, Walls of the tionof a said carbonaceous cup and its volume materially re-' 14. In anelectrical contact, the combinagraphite body and a metallic container,said graphite body having a portion thereof inclosed by the containerand held therein by expansive pressure oft-he inclosed f portion againstthe Walls of the container, said inclosed portion having a co-eflicientof expansion, greater than that of the container.

15. In an electrical contact, the combination of a cylindrical graphitebody and a metallic cup, said graphite body being compressed Within saidcup and maintained therein by expansive pressure against the Walls ofthe cup:

CHAS-H PFEIFFER. 'Witnesses:

F. FREMONT BURNHAM, FRANK A.

WASSON.

